Our asthma research program involves both exposure assessment and prevention components, and focuses on the relationship between exposure to common indoor allergens and asthma prevalence/morbidity. The National Allergen Survey, a descriptive study of allergen types and levels in floor and bedding dust in the nation's housing, is the first study to provide estimates of allergen exposure in the U.S. population. It encompasses 831 homes in 75 primary sampling units located throughout the country. The major endpoints are measurements of dust mite, cockroach, cat, dog, mouse, rat and fungal allergen levels, and endotoxin in dust samples collected from an array of sites in the surveyed homes. Results from analysis of dust mite allergens suggest that approximately 24% of U.S. homes have beds that contain >10 microgram dust mite allergen/gram dust (a level previously associated with symptomatic asthma) and approximately 46% of U.S. homes have beds that contain >2 microgram dust mite allergen/gram dust (a level previously associated with mite allergen sensitization). The likelihood of having a high dust mite allergen level in the bed was greater for older homes, non-western region homes, lower income households and bedrooms with higher humidity. Detectable cockroach allergen is present in approximately 6% of U.S. homes. The likelihood of having a high bed cockroach allergen levels was greater for lower income households, homes with evidence of moisture, and homes with evidence of food debris. This nationally representative survey will (a) provide current estimates of indoor allergen exposure in the U.S. population, (b) establish a database that can be used to stimulate future studies which attempt to correlate allergen exposure to disease outcome, (c) provide a baseline that can be used as a reference point for future allergen surveys, and (d) facilitate evaluation of regional, ethnic, socioeconomic, and housing characteristic differences in the allergen burden. We have also conducted a randomized clinical trial to test the feasibility/effectiveness of environmental interventions in reducing dust mite and cockroach allergen levels in inner-city North Carolina and Boston homes. Our study demonstrates that the combination of cockroach extermination and intensive cleaning can significantly reduce cockroach allergen levels in highly infested homes. Moreover, the effect can be maintained for up to 12 months with continued extermination. We have also demonstrated that steam cleaning combined with chemical treatments can significantly reduce dust mite allergen levels in carpeting. The results of these studies will be used to design a prevention trial to determine if environmental intervention aimed at reducing indoor allergen levels in homes can prevent sensitization and decrease the prevalence and morbidity of asthma in high risk children.